Plastic injection molding processing has the advantages of simple technology, high production efficiency, accurate size of a product and the like and is capable of forming the product with a complicated appearance at one time within a relatively short time. A plasticizing injection apparatus is one of core structures of an injection molding device. The performance of the plasticizing injection apparatus directly influences the injection molding efficiency, the production cost, the production environment and the like, and also has a decisive influence on the quality of an injection molded product.
For traditional screw and plunger type injection molding machines, a single-screw extrusion feeding apparatus which is used for plasticization only is added on a plunger type injection apparatus. Material shall be plasticized by a single-screw plasticizing apparatus firstly and then enters an injection material barrel through a check valve; and when a feeding quantity reaches a metering value, a plasticizing screw stops rotating, and an injection plunger starts to perform injection. The problem of this mode is that more retarded materials often exist in the material barrel, and cleaning of the material barrel is not convenient. Because two material barrels (a plasticizing material barrel and an injection material barrel) are needed, the volume of the machine and the amount of parts are increased, and the manufacturing cost is high. Moreover, the total energy consumption is increased because two heating systems are needed to heat the screw plasticizing system and a plunger injection system respectively.
For a traditional reciprocating screw type injection molding machine, the injection plunger is cancelled, and the screw has double functions of plasticization and injection at the same time, so that the screw needs to perform rotary movement to finish plasticization of the materials and also needs to perform reciprocating axial movement for injection at the same time, greatly increasing the complexity and the difficulty of the entire system and the manufacturing cost, the use cost and the maintenance cost. Moreover, during plasticization, with the axial movement of the screw, an axial temperature difference formed by molten material temperatures is relatively large and is difficult overcome.
The traditional injection machines also have one characteristic that the screw is generally adopted to plasticize the materials. Although plasticization with the screw has advantages, the screw has the disadvantages of poor plasticization capability, poor crushing capability and poor extrusion capability with respect to some materials.
For the problems of the traditional injection machines, although many researchers make researches, the researches are limited to local changes of the screw, the plunger, a control system or other components only and do not solve the above fundamental problems of the entire system. Therefore, the entire structure and the action principles thereof must be changed, so as to realize entire and fundamental improvement.
Some researches introduce vibration into the field of plastic processing molding, and optimize the extrusion process by utilizing influences of vibration of the screw on material plasticization and extrusion processes, so as to improve the quality of an extruded product.
Other researches utilize vibration of the plunger or a piston to achieve the purpose of optimizing the plasticization, the extrusion and the injection. Foreign literatures [1, 2] introduce a developed rheological injection moulding machine. A polymer melt is injected into a vibration cavity from the material barrel under the action of the screw firstly; the direction of a valve is switched; and vibration is applied by the piston; and then, the polymer melt is injected into a mould cavity by the piston, and the pressure vibration action is continuously applied to the melt before a mould gate is frozen while the pressure is maintained.
To sum up, in the existing researches on introduction of vibration into the injection and extrusion processes, in some researches, vibration is applied to the screw to optimize the injection and extrusion processes; and in some researches, vibration is applied to the plunger or the piston which is not installed in one machine barrel with the screw, so as to influence the polymer melt and further improve the performance of a final product.